1. Field of the Invention
This invention relates to a sealing apparatus for rotating shafts, in particular a stern tube seal for a ship's propeller shaft, with or without shaft bushings, in particular stern tube seals for a ship's propeller shafts, with or without shaft bushings, with gaskets, preferably a rotating mechanical seal, located in a stationary support system and in sealed contact with the shaft, and with a backup seal located in the support system equipped with a ring-shaped expandable body, into which, in the event of the failure of the main seal, a hydraulic or pneumatic pressure medium can be introduced, which activates the backup seal.
2. Background Information
In the sealing devices of this type as disclosed by Laid Open Federal Republic of Germany Patent Application Number DE 32 20 595 C2, the backup seal is designed as a type of rotating mechanical seal, with two ring-shaped discs rigidly connected to the shaft and at some distance from one another, between which ring-shaped discs there ar two rotatably mounted seal rings, which seal rings are kept at a distance from one another by an elastic ring part having a wedge-shaped cross section.
On the outside of the elastic ring there is a ring-shaped expandable body which, when the backup seal is inactive, is held at a distance from the elastic ring. When the backup seal is activated with pressure outward, the ring-shaped expandable body comes into contact with the elastic ring, and thus presses the seal rings tight against the ring-shaped discs.
Such a sealing device, of course, produces a sufficient sealing effect at relatively low pressures of the medium to be sealed out, but at higher pressures, e.g. those which occur with deep-diving watercraft, the sealing action may no longer be sufficient.
In a similar sealing device for stern tubes of ships disclosed in Laid Open Federal Republic of Germany Patent Application Number 26 39 144, the backup seal is equipped with a ring housing oriented coaxially to the shaft, and which ring housing is mounted on the shaft so that the ring housing can rotate in relation to the shaft, but the ring housing is braked by lip seals so that during normal operation the ring housing rotates along with the shaft. Outside this ring housing, there is a ring-shaped expandable body which, during normal operation, is at some distance from the ring housing, and in the event of a failure of the main seal, the expandable body is pressed tightly against the housing and brings it to a stop. It is apparent that such a backup seal having such a complicated design is not only complex and expensive to manufacture and install, but on account of the different gaps to be sealed, it is also susceptible to leaks at higher pressures of the medium to be sealed out.